The practice has much experience in constructing vehicles with acceleration elements which have been designed as hydrodynamic torque converters. In order to reduce the hydraulic losses in the zone of the hydrodynamic torque converter, or better, to eliminate such losses, a belief took hold of adding to the torque converter a so-called converter-bypass clutch. In the engaged condition of a converter-bypass clutch, a torque transfer will be bypassed around the converter into the drive string of a vehicle so equipped. The torque transfer is done principally with little loss by a restraining force based on a frictional grip resistance.
Fundamentally, two different system groups of acceleration arrangements are employed, which include a torque converter and a corresponding converter-bypass clutch.
In the case of a first system, the hydraulic activation of the converter-bypass clutch is integrally inserted into the hydraulic circuit of the corresponding hydraulic torque converter, where the first system becomes designated as a two-line converter. A converter clutch piston, which is provided for activation of the converter-bypass clutch and can be subjected to hydraulic pressure of such a two-line converter, is designed as a flexible disk, the hub of which is rotationally fixed to the turbine of the hydrodynamic torque converter.
When the converter-bypass clutch is disengaged, the converter clutch piston will receive pressure from a flow of hydraulic fluid leaving the inlet side of the hydrodynamic torque converter. The hydraulic stream flows in the direction of the back-flow side of the hydrodynamic torque converter. That is to say, the clutch piston is immersed in this flow. In order to engage the converter-bypass clutch, the inlet pressure of the of the hydrodynamic torque converter, principally, is reduced to zero, i.e., is so shifted, that an existing static total pressure in the hydrodynamic torque converter likewise drops to zero. The converter clutch piston, which is selectively placed in its closing direction of the converter-bypass clutch and is provided on that side which is remote from the hydrodynamic torque converter with a friction surfacing, in the last named operational situation of the hydrodynamic torque converter, is pressed by the spring device of the converter clutch piston against the housing of the pump-side of the hydrodynamic torque converter.
In order to increase the transfer capability of the converter-bypass clutch and therewith also to increase the transferable torque which can be directed over the converter-bypass clutch, the inlet pressure of the converter-bypass clutch is raised. The raising of the inlet pressure of the converter-bypass clutch increases the pressure of the converter clutch against the housing of the pump-side of the hydrodynamic torque converter. Conversely, in a case of an engaged converter-bypass clutch, the hydraulic fluid flow is diminished through the hydrodynamic converter to a predetermined minimum, so that essentially, the task of being a conventional, hydraulic, non-return check valve is thrust upon the piston of the converter bypass clutch.
To avoid a degradation of driving comfort, the converter-bypass clutch is advantageously engaged in such operational situations of the drive string, where disorders in the vehicle occur, which are detectable by the driver at least acoustically and are caused by rotational non-uniformities in the internal combustion motor being transferred without correction to the drive string. As a preventive measure thereagainst, it is attempted to achieve the goal of engaging in the quickest possible manner by the converter-bypass clutch for the reduction of the occurring hydraulic loss values in the hydrodynamic converter during an acceleration procedure.
DE 198 58 541 A1 makes known an electronic-hydraulic control apparatus of an automatically shifted motor vehicle, which includes an arrangement for the operation of an existing two-line converter designed as a first system group. That is to say, this would be a hydrodynamic torque converter and a corresponding converter-bypass clutch.
DE 10 2005 016 495.1 likewise teaches of a hydraulic control system for a two-line converter in which is exhibited a by-need activation of a two-line converter having a solenoid valve with a pressure control valve co-acting therewith. A control system of the cited invention is assembled with a solenoid valve and with a variable pressure control valve operationally connected thereto, where the valve disk thereof is designed with pressure reactant surfaces, resulting in having a pilot pressure, respectively, controllingly placed in opposition to a spring arrangement.
Additionally, the solenoid valve and the pressure control valve are equipped with a plurality of inlet or outlet control valves (hereinafter designated as “apertures”, which are bound with control lines, where the control lines, for the purpose of supplying hydraulic fluid pressure to the torque converter and to the converter-bypass clutch, which pressure acts against the remote end faces of the aperture mechanisms, and whereby the control lines can be subsequently connected with both the torque converter and the converter-bypass clutch. A supply pressure aperture of the solenoid valve, which is subjected to pressure, can be brought into a working connection with an operational pressure aperture of the solenoid valve, which latter aperture is in communication with the inlet side of the torque converter.
Further, there exists a difference between a control space of the solenoid valve, which can be made to envelope the supply aperture, and the bordering, pressure-responsive surfaces of the valve stem of the solenoid valve, so that the through-flow through the torque converter can be regulated by disengaged converter-bypass clutch.
From Automobiltechnischen Zeitschrift (Journal of Automotive Technology) 97 (1995), No. 10, pp. 698-706, “Electro-hydraulic control and external shifting of the WSA 330/580 automatic transmission by Mercedes-Benz” discloses an apparatus for the operation of a forward acceleration arrangement with a hydrodynamic torque converter with a corresponding converter-bypass clutch. The activation of the converter-bypass clutch is separately laid out with respect to the hydraulic fluid circulation system of the torque converter. The piston space of the converter-bypass clutch is subjected to pressure from a control line, which is separated from the hydraulic fluid through-put zone of the torque converter and which control line employs that pressure which is necessary for the activation of the converter-bypass clutch, while the converter-bypass clutch, as in a two-line converter, is spatially integrated within the housing of the torque converter. Forward acceleration movement apparatuses of this kind have been designated in practice as “three-line converters” and at present have been classified into the second system group.
This apparatus possesses, however, a system related disadvantage in that the pressure in the torque converter is opposed by the activation-pressure in the piston space of the converter-bypass clutch. This is true in the disengagement of the converter-bypass clutch. However, the pressure is undefined when the converter-bypass clutch is engaged. Hence, a desired transmission capability of the converter-bypass clutch by the above mentioned activation pressure during variations thereof in the torque converter, leads to poor uniformity in continuity of the output drive torque of under conditions which cannot be ameliorated, especially when exceeding the full operational range of the torque converter, all of which leads to reduced driving comfort.
By a wide margin, the embodiments for acceleration apparatuses, known to the practice, possess a torque converter and a corresponding converter-bypass clutch. In such cases, the clutch is hydraulically activated and is placed separately away from the torque converter. This assembly belongs to the second system group, where the converter-bypass clutch can be spatially distanced at an optionally selected position in the drive string of a vehicle. The clutch, in this position, for instance, can be employed as a shifting clutch or, alternately, as a brake within the housing of a transmission apparatus. Embodiments designed in this way exhibit an advantage over three-line converters in that the power transmission capability of the converter-bypass clutch is not supported by the internal pressure of the corresponding torque converter.
A disadvantage, however, lies in the fact that the torque converter can only be bypassed by the torque converter-bypass clutch, which is spatially distanced from the torque converter by an extremely intensive design effort which, in the zone of the input zone of a transmission apparatus, additionally requires considerable measures regarding sealing of the transmission.
The present invention thus has the purpose of making an apparatus available for the operation of a hydrodynamic torque converter and a corresponding converter-bypass clutch by which a properly engineered, simply assembled, three-line converter can be operated without a reduction in driving comfort.